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Thiago Alvarez2019-09-27 22:38:04
Computer networks
Thiago Alvarez, 2019-09-27 22:38:04

Routing loop in OSPF EIGRP redistribution?

There are two different networks with different routing protocols.
A loop has occurred in the OSPF network.
In show ip route, the ROUTER marked in blue shows a route through a completely different router that does not belong to this route at all.
I noted on the screen, that is, it should go to the right to (100.100.100.2) , and it goes to the left to (90.90.90.1) .

O E2    62.62.62.0 [110/20] via 90.90.90.1, 00:21:45, GigabitEthernet1/0
     64.0.0.0/24 is subnetted, 1 subnets
O E2    64.64.64.0 [110/20] via 90.90.90.1, 00:21:45, GigabitEthernet1/0
     66.0.0.0/24 is subnetted, 1 subnets
O E2    66.66.66.0 [110/20] via 90.90.90.1, 00:21:45, GigabitEthernet1/0
     68.0.0.0/24 is subnetted, 1 subnets
O E2    68.68.68.0 [110/20] via 90.90.90.1, 00:21:45, GigabitEthernet1/0

but it should be via 100.100.100.2
5d8e642f975e1851718653.png
UPD
So it turns out that all routers that are connected to the blue router (by the way, it is DR) send DBD packets with information about networks that originated in the EIGRP network.
That is, DR sends everyone information about EIGRP networks, and they return to him, and he thinks that the route lies through them and chooses the best one. At the moment it has selected 90.90.90.1 .
Although before that it was via 80.80.80.1, which is also wrong
How to remove the loop?

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2 answer(s)
V
Valentin, 2019-09-27
@vvpoloskin

Is there a static route on router29 by any chance at 62.62.62.0/24? If not, then you need to understand what route to this network is on it and where it came from.

A
Andrey Barbolin, 2019-09-27
@dronmaxman

I would change the metric on all routers except 31
. When you redistribute between to IGP you need to think of the routes coming back with better AD. There are few ways to filter that:
1) Applying distance to the routes coming from different IGP. EG you redistribute OSPF to RIP - you can apply AD (distance) 121 to these routes on router rip process so those would not be preferred to internal routes. Same within other IGP
2) Distribute list - you can filter out networks of particular IGP (eg EIGRP AS running it's own subnet) to come from different IGP. So you just apply distribute list and block incoming subnets which should be originated within this IGP
3) Route-map doing the same as above with the ability to add some specific filters. EG you can set tag to outgoing redistributed routes (EG set tag 90 or 170 to routes redistributed from EIGRP to OSPF). Then you with similar route-map filter routes with this tag from coming back

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